honestly this is a hard one. this is one of those fixes that 10 people can give advice and you just keep buying parts until you figure it out. the most common problem for an EVAP leak is a bad gas cap. the gasket around the cap gets brittle and no longer does it's job of staying sealed. you can pull off the cap and do a visual inspection of it. most likely this is not the problem because your code is throwing a large EVAP leak and i've only seen it throw small EVAP leaks. however, anythings possible. once you've eliminated that i would then start my way from the trunk(removing the trunk liner) and follow the lines all the way from under the car to the hood. look for anything out of the ordinary. hoses disconnected, hoses cracked pretty bad, odor of gas strong somewhere. just because is says the shut off valve is stuck closed doesn't mean you need a new valve. if you can't figure anything out you really need to have a shop perform a smoke test to determine the leak. good luck and let us know

Say it is a bad gas cap. How long would it take for the engine light to go off? I'm in Texas and was supposed to drive up to Chicago (saw you're from there) today. How big of a problem is it? I don't see any gas leaking nor do I smell gas.